1. Field of the Invention
The present invention relates to an epi-illumination apparatus used in a fluorescence microscope or a microscope for industrial use etc.
2. Related Background Art
Generally, the epi-illumination apparatus of a microscope is provided with a halogen lamp or a discharge tube, such as an Hg discharge tube or an Xe discharge tube, etc as a light source. The halogen lamp has a light emitting surface of the size of about 3 mm to 5 mm, while the discharge tube such as an Hg or Xe discharge tube has a light emitting area of the size of about 0.3 mm to 0.5 mm. On the other hand, the size of the pupil of an objective lens to be illuminated is about 16 mm at largest. Therefore, in the epi-illumination apparatus using the halogen lamp, the magnification of the light source (i.e. the magnification at which the light source is magnified) is set to about 4× so that substantially whole of the pupil of the objective lens would be illuminated with the illumination light. On the other hand, in the apparatus using the Hg or Xe lamp, the magnification of the light source in the illumination apparatus must be set to a higher magnification, and in general the magnification is set to about 10×.
Recently, demand for an epi-illumination apparatus in which both the Hg lamp and Xe lamp can be used has been raised in order to allow inspection of a specimen in various observation methods. In order to meet this demand, Japanese Patent Application Laid-Open No. 6-289301 proposes a structure that enables use of both a halogen lamp and an Hg lamp in one single epi-illumination apparatus by inserting/withdrawing a variable magnification optical system in the form of a substantially a focal system into/from a space between a lamp house and an epi-illumination light projecting tube to thereby vary the magnification of the light source.
However, the size of the above-mentioned epi-illumination apparatus disclosed in Japanese Patent Application Laid-open No. 6-289301 is large, since the optical path length of its entire illumination optical system is extended in order to allow the insertion and withdrawal of the substantially a focal optical system between the lamp house and the epi-illumination light projecting tube for varying the magnification of the light source.